User's Manual

LISA-U1/LISA-H1 series - System Integration Manual
3G.G2-HW-10002-2 Advance Information Design-In
Page 100 of 116
Application Board Antenna Assembly
Diagnostic Circuit
LISA-U1/LISA-H1 series
ADC
Current
Source
RF
Choke
DC
Blocking
Front-End
RF Module
RF
Choke
DC
Blocking
Radiating
Element
Zo=50 Ω
Resistor for
Diagnostic
Coaxial Antenna Cable
ANT
Figure 58: Antenna detection circuit and antenna with diagnostic resistor
Examples of components for the antenna detection diagnostic circuit are reported in the following table:
Description
Part Number - Manufacturer
DC Blocking Capacitor
Murata GRM1555C1H220JA01 or equivalent
RF Choke Inductor
Murata LQG15HS68NJ02, LQG15HH68NJ02 or equivalent (Self Resonance Frequency ~1GHz)
Resistor for Diagnostic
15 k 5%, various Manufacturers
Table 36: Example of components for the antenna detection diagnostic circuit
Please note that the DC impedance at RF port for some antennas may be a DC open (e.g. linear monopole) or a
DC short to reference GND (e.g. PIFA antenna). For those antennas, without the diagnostic circuit of Figure 58,
the measured DC resistance will always be at the limits of the measurement range (respectively open or short),
and there will be no mean to distinguish between a defect on antenna path with similar characteristics
(respectively: removal of linear antenna or RF cable shorted to GND for PIFA antenna).
Furthermore, any other DC signal injected to the RF connection from ANT connector to radiating element will
alter the measurement and produce invalid results for antenna detection.
It is recommended to use an antenna with a built-in diagnostic resistor in the range from 5 kΩ to 30 kΩ
to assure good antenna detection functionality and to avoid a reduction of module RF performance. The
choke inductor should exhibit a parallel Self Resonance Frequency (SRF) in the range of 1 GHz to
improve the RF isolation of load resistor.
For example:
Consider a GSM antenna with built-in DC load resistor of 15 k. Using the +UANTR AT command, the module
reports the resistance value evaluated from ANT connector to GND: